Evaluation of Levelized Cost of Electricity Generated From Hot Spring Geothermal Resources in Nigeria: A Case Study of Rafin Reewa Hot Spring, Lere Local Government of Kaduna State

Evaluation of Levelized Cost of Electricity Generated From Hot Spring Geothermal Resources in Nigeria: A Case Study of Rafin Reewa Hot Spring, Lere Local Government of Kaduna State

Chapter One

OBJECTIVE OF THE STUDY

The main aim of this research work is to establish the levelised cost of electricity generation  by  using  ―low  temperature‖  geothermal  resource  from  Rafin  Reewa  hot springs.

The cost of geothermal power is, obviously, dependent upon the technology employed in bringing geothermal energy to the surface and converting it to electricity. Consequently, the specific objectives of this research work are as follows:

1. To determine the reservoir
2. To select energy conversion (EC) systems appropriate for Rafin Reewa hot spring needed to demonstrate feasibility of geothermal power plant at a commercial-scale.
3. To determine the effects of mass flow rate as well as resource depth on the levelised cost of power generated using geofluid from Rafin Reewa hot
4. To estimate the Levelised Cost of power generation from Rafin Reewageo thermal

CHAPTER TWO

LITERATURE REVIEW

INTRODUCTION

This section will describe the basic concept of geothermal energy and its conversion technologies. The section also x-rays the Nigeria geological setting as well as that of the study. The various geothermometers used to determine the temperature of the study area were reviewed. The economics and technological factors that influences the calculations of levelised cost of electricity (LCOE) will also be describes in this chapter, followed by an explanation of how the software used in the study work generate the LCOE.

GEOTHERMAL ENERGY

In a simple term, geothermal energy is ―energy from the Earth‖. Geothermal energy, the natural heat within the earth, arises from the ancient heat remaining in the Earth’s core, from friction where continental plates slide beneath each other, and from the decay of radioactive elements that occur naturally in small amounts in all rocks (Antonia et al., 2012). The Earth‘s core is molten with an average temperature of ~4000^oC, and this heat is continuously being lost at the surface to the atmosphere creating an increase in temperature with depth called the geothermal gradient. The transfer of heat from the core occurs primarily through solid rock by conduction and secondly through convection in areas with fluid interaction (i.e. water, magma, salt diapers) (Kimball, 2010). The Earth‘s interior heat energy is estimated to be equivalent to 42 million megawatts (MW) of power, and is expected to remain so for billions of years to come, ensuring an inexhaustible supply of energy (Alyssa, 2007).

Heat energy is in all material on the earth, since the only matter without heat is at a temperature of absolute zero. The temperature of the earth’s surface is controlled by the level of radiation from the sun, the filtering and insulating effects of the atmosphere, the local vegetation cover and the annual cycle of seasons (Jessop, 2008). The annual average temperature of the surface of the earth normally lies between -15^OC, in regions near the poles, and 30^OC, in equatorial regions. Apart from perturbations of up to 4^OC near the surface, due to rapid surface warming in the last 100 to 200 years, temperature in the solid earth increases with depth (Jessop, 2008).

Thermal energy in the earth is distributed between the constituent host rock and the natural fluid that is contained in its fractures and pores at temperatures above ambient levels. These fluids are mostly water with varying amounts of dissoblved salts; typically, in their natural in situ state, they are present as a liquid phase but sometimes may consist of a saturated, liquid-vapor mixture or superheated steam vapor phase. The amounts of hot rock and contained fluids are substantially larger and more widely distributed in comparison to hydrocarbon (oil and gas) fluids contained in sedimentary rock formations underlying the earth. (The NEED Project, 2011)

A geothermal system requires heat, permeability, and water. The heat from the earth‘s core continuously flows outward. Sometimes the heat, as magma, reaches the surface as lava, but it usually remains below the earth‘s crust, heating nearby rock and water, sometimes to levels as hot as 700°F. When water is heated by the earth‘s heat, hot water or steam can be trapped in permeable and porous rocks under a layer of impermeable rock and a geothermal reservoir can form. This hot geothermal water can manifest itself on the surface as hot springs or geysers, but most of it stays deep underground, trapped in cracks and porous rock. This natural collection of hot water is called a geothermal reservoir (Kimball, 2010).

Geologic processes, specifically plate tectonics, control the concentration of the earth‘s heat. Volcanic activity and the presence of magma near the surface occurs at tectonic plate boundaries and over mantle hot spots of volcanism which explains the concentration of geothermal energy production in regions such as the Pacific Ring of Fire as shown in figure 2.2 (Kimball, 2010).

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CHAPTER THREE

MATERIAL AND METHOD

INTRODUCTION

This section described the methodology adopted for the research work. The chapter will also explained how the various geothermometry equations established in the literature review are used in the calculation of the temperature of the geofluid of the Rafin Reewa hot spring (the study area). The LCOE will be evaluated using GETEM software and thereafter the result obtained will be presented in tabular form.

 METHODOLOGY

The aim of this project is to arrive at the levelised cost of producing geothermal power using Rafin Reewa hot spring. To accomplish the specific objectives of the work:

2. The resource temperature at the study area is determined using the empirically and thermodynamically derived cations geo thermometers by applying the geochemical analysis of Rafin Reewa hot spring waters that was established by Schoeneich in table 5.
3. Parameters and variables

Since there is no extensive geothermal energy research and development at the study area, the values of parameters and variables are based primary on values established in the literature of the study area and the world in general.

Mass Flow Rate

The geothermal mass flow is required to calculate the available thermal power of the plant. The literature review of this study has shown that the flow of the geothermal fluid from hot springs range from 0.56 to 500 kg/s (see table 2.6). It is therefore of great     interest to investigate the LCOE for a hot spring binary power plant for different geothermal mass flows. Couples with this, for geothermal power project to be    economically optimized, high mass flow rates of hot water are needed. Low flow rates result in heat loss to a shallow, cooler subsurface region. Consequently, the flow rates of 100kg/s, 200kg/s, 300kg/s and 400kg/s were selected for analysis.

CHAPTER FOUR

RESULTS AND DISCUSSION

INTRODUCTION

This section will discuss the various results obtained in the course of evaluating the levelised cost of electricity.

 

CHAPTER FIVE

SUMMARY, CONCLUSION AND RECOMMENDATION

SUMMARY

1. The study established that the temperature of the geofluid at the study area is14^oC
2. It is possible to generate electricity from the geofluids at Rafin Reewa hot springby using standard air-cooled binary-cycle technology.
3. Levelised cost of electricity (LCOE) analysis carried out using a GeothermalElectricity Technology Model (GETEM) indicates that well output (production flow rate), resource temperature and resource depth have a direct relationship with the levelized costs of electricity.
4. Analysis shows that both the flow rate and resource depth affect the LCOE withflow rate having the most significant
5. The analysis of this study indicates that there is a direct relationship between thevarious cost factors and levelised cost. This direct relationship of the various factors to the levelized cost means that the levelized cost can be optimized by undertaking cost factor selection so as to obtain the least cost factor combination.
6. If the reservoir were able to supply only 100 kg/s at depth, the plant cost wouldvary from $663,609,961 to $694,939,597 (N132, 721,992,200 – N138, 987,919,400) for 50MW plant capacity depending on depth.
7. Brine effectiveness (plant performance) influenced the levelised cost of electricity
8. If a mass flow rate of 100 kg/s can be sustained from the 120°C reservoir, the costof power plant will be less but with high present value of power
9. Lowest cost of electricity of 43.010cent/kWh (N86.02/kWh) could be achievedwith a flow rate of 100 kg/s and depth of 1000m from a 122.14°C Rafin Reewa hot spring reservoir using an air-cooled binary
10. Comparingthe lowest LCOE obtained by this research study with other competitive power technologies available in Nigeria, the LCOE of 43.010cent/kWh (N86.02/kWh) is high but low when compare with the LCOE of solar CSP and PV technologies. Under these circumstances, it appears that low grade geothermal energy could be a practical source of power. While it is expected that a geothermal power project in Nigeria would use a binary cycle plant and thus would not emit any steam.

CONCLUSION

A study has been carried out at Rafin Reewa hot spring with the aim of evaluating the levelised cost of electricity generated from the resource located at the study area.

Using cations geothermometers, the study shows that the temperature of the geofluid at the study area is 122.14^oC. Hence, this indicates that electricity can be to generate from the geofluids at Rafin Reewa hot spring by using standard air-cooled binary-cycle technology.

Through the use of Geothermal Electricity Technology Model (GETEM), the study established that both the mass flow rate and the resource depth have significant effect on Levelised cost of electricity (LCOE). But mass flow rate has more impact on the LCOE than the resource depth. In conclusion, the study shows that the levelised cost of electricity (LCOE) using the resources at the study area is 43.010cent/kWh (N86.02/kWh) at a flow rate of 100 kg/s and depth of 1000m from a 122.14°C Rafin Reewa hot spring reservoir using an air-cooled binary system.

Although levelised cost of energy as indicated by this study is currently high and the prevalence of installed and operating geothermal power plants is still somewhat limited, great potential for advancement of geothermal systems still exists.

While research on the geothermal potential in Rafin Reewa is still in the infant stage, several factors analyzed in this report appear very promising for the future. With an appropriate amount of funding, more conclusive evidence of this potential can be unearthed through research and eventual development. After all, the ability of a geothermal facility to provide consistent, base-load power cannot be ignored.

RECOMMENDATIONS

1. In arriving at the results of this study, no consideration was given to the optimumwater withdrawal rates in relation to the size of the reservoir, the amount of heat flow in the reservoir or the possibility of soil subsidence in the study area. The study of this aspect may be significant value prior to the actual exploitation. Hence, it is recommended that these parameters should served as research area for further
2. It is obvious that the cost data used in this study is time dependent. As the pricesof various items in the exploitation, confirmation, well field development and other aspect change, the cost of power will be affected, in some cases quite  Hence, it is recommended that this study be periodically updated.
3. The potential of geothermal energy in evolving Nigerian energy markets is largeand warrants a comprehensive research and demonstration effort to move this technology to commercial viability, especially as the country approaches a period when gap between demand for and generation of electricity is coming wider by
4. The analysis shows that the development of new geothermal energy resources willnot be limited by the size and location of the resource in Nigeria, and it will occur at a critical time when grid stabilization with both replacement and new base-load power will be needed. Adding the geothermal energy option to the Nigeria energy portfolio will reduce growth in natural gas consumption and slow the need for adding/maintaining the fossil fuel facilities to handle Nigerian cripple power
5. Aswe expect that the cost of power potential demonstrated in this study warrants a comprehensive research and demonstration effort to begin moving toward the period when replacement of retiring fossil and new capacity growth will most affect the Nigerian electrical supply.
6. While the results presented in this study are applicable to the study site conditionsselected for analysis and the selected variables, the result can be easily adapted to incorporate the conditions at any similar location. The specific site conditions can be updated to reflect the specific conditions, and the levelised cost of electricity can be evaluated to reflect the conditions at that location.
7. Recognizing that current flow on renewable energy technologies is inadequate, itis recommended that demonstration projects on various renewable energy forms be widely established especially geothermal energy; so that the performance and efficiency with which services are delivered can be calculated and sensitized.

CONTRIBUTION TO KNOWLEDGE

The study established that:

1. Thegeofluid temperature and LCOE of 010 cent/kWh (N86.02/kWh) are suitable for an air-cooled binary geothermal power plant at Rafin Reewa hot spring at a flow rate of 100kg/s and a resource depth of 1000m.
2. The total plant cost, exclusive of exploration wells, for an air-cooled binary powerplant of 50MW for Rafin Reewa hot spring is $663,609,961 (N13, 272,198,200) at a flow rate of 100kg/s and a depth of 1000m.
3. The study informs the ongoing debate of how to provide a more sustainable andsecure energy supply for Nigeria for the long term, without compromising our economic capacity and political and social stability, and while minimizing environmental

 LIMITATIONS

1. Thestudy didn‘t establish the amount of geofluid reserve of the Rafin Reewa hot spring.
2. Insufficient literatureson geothermal energy technologies of hot springs in

 

REFERENCES

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